Reason for harvest moon phenomenon

Dear forum,

I just read some postings about the harvest moon phenomenon but I´m
still not quite sure about one point : Is the fact that the moons
orbit comes close to the ecliptic at the autumnal equinox related to
the inclination of our earth´s axis (is it a kind of seasonal effect
then), or is it just caused by the nature of the moons orbit itself ?
Thanks for your input !

Jörg

Joerg Sczepek wrote:

Dear forum,

I just read some postings about the harvest moon phenomenon but I´m
still not quite sure about one point : Is the fact that the moons
orbit comes close to the ecliptic at the autumnal equinox related to
the inclination of our earth´s axis (is it a kind of seasonal effect
then), or is it just caused by the nature of the moons orbit itself ?
Thanks for your input !

Jörg



Keith's Harvest Moon Page
http://home.hiwaay.net/~krcool/Astro/moon/harvest/

On 17 Aug 2004 16:45:23 -0700, (Joerg Sczepek) wrote:

I just read some postings about the harvest moon phenomenon but I´m
still not quite sure about one point : Is the fact that the moons
orbit comes close to the ecliptic at the autumnal equinox related to
the inclination of our earth´s axis (is it a kind of seasonal effect
then), or is it just caused by the nature of the moons orbit itself ?
Thanks for your input !

What phenomenon?

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Chris L Peterson" wrote in message

What phenomenon?

You haven't noticed?

:^0

Joerg Sczepek wrote:
I just read some postings about the harvest moon phenomenon but I'm
still not quite sure about one point : Is the fact that the moons
orbit comes close to the ecliptic at the autumnal equinox related to
the inclination of our earth's axis (is it a kind of seasonal effect
then), or is it just caused by the nature of the moons orbit itself ?

The Moon simply orbits in a plane that is close to the ecliptic. It is
*always* within about 5 degrees of the ecliptic, no matter what time of
year it is, no matter what phase it is.

The Harvest Moon "phenomenon" is simply that the ecliptic is ascending
(with respect to the celestial equator) where the September Full Moon
is, so as the Moon follows that portion of the ecliptic, it rises at an
earlier time than it would if it were following the descending portion
of the ecliptic. (Just as the Sun rises earlier when it rises further
north, and later when it rises further south.) Thus, the time between
successive moonrises can be as short as 25 minutes at a latitude of 40
degrees north. (Well, 25 minutes plus 24 hours!)

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

(Brian Tung) wrote in message ...

The Moon simply orbits in a plane that is close to the ecliptic. It is
*always* within about 5 degrees of the ecliptic, no matter what time of
year it is, no matter what phase it is.

The Harvest Moon "phenomenon" is simply that the ecliptic is ascending
(with respect to the celestial equator) where the September Full Moon
is, so as the Moon follows that portion of the ecliptic, it rises at an
earlier time than it would if it were following the descending portion
of the ecliptic. (Just as the Sun rises earlier when it rises further
north, and later when it rises further south.) Thus, the time between
successive moonrises can be as short as 25 minutes at a latitude of 40
degrees north. (Well, 25 minutes plus 24 hours!)


So if I sum up what I unnderstood so far, in the northern latitudes
the moon seems to follow the ascending part of the ecliptic close to
the autunmal equinox (and thus takes a shallow path that minimizes the
time difference between successive risings), because of the relation
of the earth´s position (inclination of it´s axis) to the moons orbit.
For an observer in the southern hemisphere the same is true close to
the vernal equinox, because the relationship is almost exactly the
other way around due to the earth´s movement. Right ?!

Joerg Sczepek wrote:
So if I sum up what I unnderstood so far, in the northern latitudes
the moon seems to follow the ascending part of the ecliptic close to
the autunmal equinox (and thus takes a shallow path that minimizes the
time difference between successive risings), because of the relation
of the earth's position (inclination of it's axis) to the moons orbit.
For an observer in the southern hemisphere the same is true close to
the vernal equinox, because the relationship is almost exactly the
other way around due to the earth's movement. Right ?!

Sort of. Technically, the Full Moon in September is always ascending,
in the sense that its moving northward in the sky. However, since the
Moon's path is inclined northward in the southern hemisphere, the Full
Moon will rise earlier there if it's actually moving *southward* in the
sky. That happens to the greatest extent around March.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt